Reinforcing additive

ABSTRACT

Sulfur containing organosilicon compounds having the formula:

This application is a continuation-in-part of application Ser. No. 277,043, filed Aug. 1, 1972, now U.S. Pat. No. 3,842,111. This is a division of application Ser. No. 415,176 filed Nov. 12, 1973 now U.S. Pat. 3,876,489.

The present invention is directed to additives for silicate or silica filler containing rubber mixtures which additives favorably influence the production of the rubber mixtures and the properties of the vulcanizate in a surprising and decisive manner. These additives belong chemically to the group of organosilicon compounds containing sulfur in the molecule. The additives impart to the silica (or silicate) fillers improved reinforcing properties and increase the over-all cross-linking of the vulcanization; they are designated as reinforcing additives in the following description.

It is known that carbon blacks generally, and especially the especially developed types of carbon black, are not present merely as fillers in rubber vulcanizate but take part in a specific manner as reinforcing fillers (active fillers). The influence of carbon black on the reinforcement of the polymers and the determination of the rubber-filler-reciprocal effect are described for example in the magazine "Kautschuk und Gummi, Kunststoffe", No. 8, pages 470-474 (1966) and No. 1, pages 7-14 (1970).

The silica (or silicate) fillers, i.e., siliceous materials as, for example, highly dispersed silica, silicates or the like are known to be different in their activity from carbon blacks. This difference is recognized by two kinds of facts. First the reinforcing effect of silica or silicate fillers is different from that of carbon black because of their completely different type of surface. Secondly, the active silica influence the vulcanization process, especially if the vulcanization is effected by sulfur and accelerator additives. Previously there have been no sulfur vulcanizations in which the silica (or silicate) fillers did not reduce the cross-linking.

In recent years there have been attempts to improve the activity of silica (or silicate) fillers by admixing chemical substances to the starting mixture.

Thus it is known to use mercaptomethylalkoxysilane as an adhesive promoter between silicate materials such as glass, clay, asbestos and silica dioxide (silica) and organic resins such as butadiene-styrene copolymers, natural rubber, polyester resins, polystyrene and styrene-maleic anhydride-mixed polymers, whereby this silane is introduced on the substrate in any desired manner and bound with the resin, see German Offenlegungsschrift No. 2,038,715.

Furthermore, there are known organosiliconsulfide compounds having a sulfidic sulfur atom between the hydrocarbon radicals which are recommended for use as adhesive promoters or also as intermediate products for compounds which can be used as water repelling agents or oxidizing agents. The named organosilicon compounds, however, can also have sulfur containing end groups such as thiocyanato, xanthogenato, thioether, thionic acid ester groups or the like, see Lee, German Auslegeschrift 1,911,227.

The organo-organooxysilanes, for example, the 3-thiocyanatopropyl-trimethoxy- or triethoxysilane, which according to Belgian patent 770,097 and Rocktaschel U.S. application Ser. No. 163,467 filed July 16, 1971 now U.S. Pat. No. 3,798,196 find outstanding use in cross-linkable or vulcanizable mixtures of organic polymers, inorganic materials and the corresponding cross-linking or vulcanization agents or systems have similar end groups. The silanes described in German Auslegeschrift No. 1,911,227, Belgian Pat. No. 770,097 and the Rocktaschel U.S. application possess only a silicon atom bound to a carbon atom or a further silicon atom bound thereto by an oxygen atom or an amino nitrogen atom.

Furthermore there are known gamma-mercaptopropyltrimethoxy and triethoxy silanes as well as beta-mercaptoethyltriethoxy silane and other sulfur free silanes, which after subsequent partial hydrolysis and coating on the surface of silica or silicate filler particles serve to facilitate the workability of rubber mixtures and improvement of the strength properties of reinforced rubber articles, Vanderbilt U.S. Pat. No. 3,350,345.

Besides there are known tire threads produced from a rubber mixture which contain a silica as a filler and a silane as coupling agent, see Belgian Pat. No. 760,099. An exceedingly large number of silanes are included in the general formula in the Belgian patent, but from the introduction, the tables and examples there can only be found gamma-mercaptopropyltrimethoxysilane as the single coupling agent tried.

The present invention is drawn to a class of organosilanes containing sulfur in the molecule which are distinguished in several respects from the numerous known silanes in their outstanding advantages in use and especially in their suitability and reinforcing additives as is described and shown below. The new additives produce in siliceous fillers (i.e., silica and silicates) containing rubber mixtures and vulcanizates unforeseen, valuable and industrially outstanding properties, whereby the rubber mixtures contain at least one rubber, a cross-linking system (e.g., including sulfur), a sulfur containing organosilane, fillers and preferably further conventional rubber additives. The invention is characterized by the rubber mixture containing as a strengthening additive one or more organosilanes of the formula:

    I Z -- alk -- S.sub.n -- alk -- Z

in which Z is: ##STR2## and in which R₁ is an alkyl group of 1 to 4 carbon atoms or phenyl and R₂ is an alkoxy group with 1 to 8, preferably 1 to 4, carbon atoms, a cycloalkoxy group with 5 to 8 carbon atoms or a straight or branched chain alkylmercapto group with 1 to 8 carbon atoms. All the R₁ and R₂ groups can be the same or different. Alk is a divalent hydrocarbon group with 1 to 18 carbon atoms. It can be straight or branched chain and can be a saturated aliphatic hydrocarbon group, an unsaturated aliphatic hydrocarbon group or a cyclic hydrocarbon group. Preferably alk has 1 to 6, most preferably 2 to 3 carbon atoms and n is a [whole] number of 2 to 6, as well as one or more siliceous fillers (i.e. silica or a silicate), in a given case in admixture with carbon black. Preferably n is 2 to 4, more preferably 3 to 4.

Preferably the rubber mixtures contain at least one organosilane, especially one or two, most preferably one, of formula I in which Z stands for the group ##STR3## in which group R₂ is an alkyl group with 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms and alk is a divalent straight chain saturated hydrocarbon radical (i.e., alkylene), having 1 to 6, preferably 2 or 3 carbon atoms. Besides the compounds named in the examples as preferred reinforcing additives, there can be used with advantage compounds of the formula ##STR4## where R₂ is OCH₃ ; --OCH₂ CH₃ ; OCH₂ CH₂ CH₃ ; ##STR5## Other preferred silanes are those wherein in place of ##STR6## in formula I, Z can be ##STR7## wherein R₁ is alkyl (branched or unbranched with 1 to 4 carbon atoms), phenyl or cyclohexyl and R₂ is as defined for formula II.

The new silanes used in the invention also have in the middle of the somewhat symmetrical molecule two or more connected sulfur atoms and two separated, to a certain degree, terminal standing silane groups. It must be accepted that this molecular structure causes the outstanding properties of the new vulcanization reinforcer.

The 3-mercaptopropyltrimethoxysilane already mentioned above in rubber mixtures which contain silica as a filler definitely increases the modulus values, tensile strength, abrasion resistance, rebound and shore hardness of the vulcanizate.

On the contrary, however, the scorch time and the Defo-elasticity of the unvulcanized mixtures are influenced unfavorably. The scorch times are shortened drastically. In the production of such mixtures even in the internal mixer frequently there occurs premature scorching which makes it impossible to further work the mixture.

The Defo-elasticity is sharply increased which means an increase of the elastic rubber portion in the crude mixture and makes more difficult the further processing, for example, by extrusion.

On the contrary, the rubber mixtures containing the new reinforcing additives employed in the present invention show definite industrial advantages in regard to the properties of the raw mixtures and the vulcanizates in comparison to those in the art. The raw mixtures now show especially a previously unknown degree of processing safety, a strongly reduced stiffness and only a slight increase of Defo-elasticity. All of these advantageous properties or effects for the first time open up the industrial use of such mixtures. The properties of the vulcanizates obtained are excellent and are comparable with the properties of correspondingly carbon black filled vulcanizates or even exceed these, as will be pointed out below. The mentioned improvement of the properties of the raw mixture and the vulcanizate for the first time opens field of use for silica fillers which previously were reserved for only carbon black as reinforcing filler.

The term "siliceous filler" is a broad term and refers to fillers which are rubber compatible or can be worked into rubber mixtures which fillers consist of silicates or silica, or contain silicates or silica and/or contain chemically bound silicates (or silica) in the widest sense, including mixtures of two or more siliceous fillers. Especially counted as siliceous fillers are:

Highly dispersed silica (silicon dioxide) having a specific surface area in the range of about 5 to 1000, preferably 20 to 400 m² /g (determined with gaseous nitrogen according to the known BET procedure) and with primary particle sizes in the range of about 10 to 400 nm. (nanometer, 10.sup.⁻⁹ meters), which can be produced, for example, by precipitation from solutions of silicates, by hydrolysis and/or oxidative high temperature conversion. There can also be used flame hydrolysis of volatile silicon halides, e.g., silicon tetrachloride, or by electric arc processes. These silicas, in a given case, can also be present as mixed oxides or oxide mixtures with oxides of the metals aluminum (alumina), magnesium (magnesium oxide), calcium (calcium oxide), barium (barium oxide), zinc (zinc oxide), zirconium (e.g., zirconium dioxide), or titanium (e.g., titanium dioxide).

Synthetic silicates, for example, aluminum silicate or alkaline earth silicates such as magnesium, or calcium silicate with specific surface areas of about 20 to 400 m² /g and primary particle sizes of about 10 to 400 nm.

Natural silicates, for example, kaolin, wollastonite, talc and asbestos as well as natural silicas, e.g., quartz or sand.

Glass fibers and glass fiber products such as mats, webs, strands, fabrics, non-woven fabrics and the like as well as microglass balls (microglass balloons).

The siliceous fillers mentioned can be added in amounts of about 10 or, in a given case, even less, up to about 250 parts by weight based on 100 parts by weight of rubber polymer.

As filler mixtures there can be used, for example, silica-kaolin or silica-glass fibers-asbestos, as well as blends of siliceous reinforcing fillers with the mentioned rubber blacks, for example, silica-ISAF carbon black or silica-glass fiber cords HAF carbon black.

Typical examples of siliceous fillers usable in the invention, for example, are those produced by Degussa, such as silica or silicates under the tradenames Aerosil, Ultrasil, Silteg, Durosil, Extrusil, Calsil, etc.

Furthermore there can be mixed into the rubber mixtures various additives which are well known in the rubber industry and widely used.

There are several advantages if the additive of the invention is not added as such to the rubber mixture but first a mixture of at least one siliceous filler and at least one organosilane of formula I above is prepared and this is then or later incorporated in the rubber mixture or the remaining components of the mixture of the rubber mixture in the customary manner with the help of conventional mixing apparatus and homogeneously distributed therein.

In the production of the master batch, there is still a fluid, dry product if there is mixed into the siliceous filler an equal or even larger amounts by weight of liquid organosilane. Consequently, it is also possible to add only a portion of the entire fillers needed to produce the rubber mixture which as a master batch already contains the entire amount of necessary silane.

Examples of organosilanes within formula I which can be used in the invention are bis[trialkoxysilyl-alkyl-(1)]-polysulfides such as bis[2-trimethoxy-, -triethoxy-, -tri-(methylethoxy)-, -tripropoxy-, -tributoxy and so forth up to -trioctyloxysilyl-ethyl]-polysulfides, namely the di-, tri-, tetra-, penta-, and hexasulfides, further the bis-[3-trimethoxy-, -triethoxy-, -tri-(methylethoxy)-, -tripropoxy-, -tributoxy- and so forth up to -trioctoxypropyl]- polysulfide, namely again the di-, tri-, tetra-, penta- and hexasulfide; furthermore the corresponding bis[3-trialkoxysilylisobutyl]- polysulfides, the corresponding bis[4-trialkoxysilyl-butyl]- polysulfides and so forth up to bis[6-trialkoxysilyl-hexyl]- polysulfides. Of those chosen, there are preferred relatively simply constructed organosilanes of formula I including bis-[3-trimethoxy-, -triethoxy-, and -tripropoxysilyl-propyl]- polysulfides namely the di-, tri- and tetrasulfides. These and the other organosilanes of formula I which can be added with good success can be made according to the process of Meyer-Simon application Ser. No. 277,043 filed on Aug. 1, 1973 which corresponds to German patent applications Nos. P 2,141,159.6; P 2,141,160.9 and P 2,212,239.9. The entire disclosure of Meyer-Simon (and the corresponding German applications) is hereby incorporated by reference. Typical examples of specific compounds within formula I which can be used in the invention include:

Examples of compounds within the invention include 3,3'-bis (trimethoxysilylpropyl) disulfide, 3,3'-bis (triethoxysilylpropyl) tetrasulfide, 3,3'-bis(trimethoxysilylpropyl) tetrasulfide, 2,2'-bis (triethoxysilylethyl) tetrasulfide, 3,3'-bis (trimethoxysilylpropyl) trisulfide, 3,3'-bis (triethoxysilylpropyl) trisulfide, 3,3'-bis (tributoxysilylpropyl) disulfide, 3,3'-bis(trimethoxysilylpropyl) hexasulfide, 3,3'-bis(trioctoxysilylpropyl) tetrasulfide, 3,3'-bis(trihexoxysilylpropyl) disulfide, 3,3'-bis(tri-2"-ethylhexoxysilylpropyl) trisulfide, 3,3'-bis(triisooctoxysilylpropyl) tetrasulfide, 3,3'-bis(tri-t-butoxysilylpropyl) disulfide, 2,2'-bis(methoxy diethoxy silyl ethyl)tetrasulfide, 2,2'-bis (tripropoxysilylethyl) pentasulfide, 3,3'-bis (tricyclohexoxysilylpropyl) tetrasulfide, 3,3'-bis(tricyclopentoxysilylpropyl) trisulfide, 2,2'-bis(tri-2"-methylcyclohexoxysilylethyl) tetrasulfide, bis(trimethoxyxilylmethyl) tetrasulfide, 3,3'-bis (trimethylmercaptosilylpropyl) tetrasulfide, 2,2'-bis(triethylmercaptosilylethyl) disulfide, 2,2'-bis(tributylmercaptosilylethyl) trisulfide, 2,2'-bis(tri sec. butylmercaptosilylethyl) trisulfide, 3,3'-bis (trioctylmercaptosilylpropyl) tetrasulfide, 2,2'-bis (trihexylmercaptosilylethyl) hexasulfide, 3,3'-bis (ethyldipropylmercaptosilylpropyl) tetrasulfide, 3-methoxy ethoxy propoxysilyl 3'-diethoxybutoxysilylpropyltetrasulfide, 2,2'-bis (dimethyl methoxysilylethyl) disulfide, 2,2'-bis(dimethyl sec.butoxysilylethyl) trisulfide, 3,3'-bis (methyl butylethoxysilylpropyl) tetrasulfide, 3,3'-bis(di-t-butylmethoxysilylpropyl) tetrasulfide, 2,2'-bis (phenyl methyl methoxysilylethyl) trisulfide, 3,3'-bis (diphenyl isopropoxysilylpropyl) tetrasulfide, 3,3'-bis(diphenyl cyclohexoxysilylpropyl) disulfide, 3,3'-bis(dimethyl ethylmercaptosilylpropyl) tetrasulfide, 2,2'-bis(methyl dimethoxysilylethyl) trisulfide, 2,2'-bis(methyl ethoxypropoxysilylethyl) tetrasulfide, 3,3'-bis(diethyl methoxysilylpropyl) tetrasulfide, 3,3'-bis (ethyl di-sec. butoxysilylpropyl) disulfide, 3,3'-bis(propyl diethoxysilylpropyl) disulfide, 3,3'-bis(butyl dimethoxysilylpropyl) trisulfide, 3,3'-bis(phenyl dimethoxysilylpropyl) tetrasulfide, 3-phenyl ethoxybutoxysilyl 3'-trimethoxysilylpropyl tetrasulfide, 4,4'-bis(trimethoxysilylbutyl) tetrasulfide, 6,6'-bis (triethoxysilylhexyl) tetrasulfide, 12,12'-bis(triisopropoxysilyl dodecyl) disulfide, 18,18'-bis(trimethoxysilyloctadecyl)tetrasulfide, 18,18'-bis (tripropoxysilyloctadecenyl) tetrasulfide, 4,4'-bis(trimethoxysilyl-buten-2-yl) tetrasulfide, 4,4'-bis (trimethoxysilylcyclohexylene) tetrasulfide, 5,5'-bis(dimethoxy methylsilylpentyl) trisulfide, 3,3'-bis(trimethoxysilyl-2-methyl propyl) tetrasulfide, 3,3'-bis(dimethoxyphenylsilyl-2-methylpropyl) disulfide.

The new silanes used in the invention can be added to the rubber mixture in amounts of 0.1 to 50 parts by weight, preferably within the limits of 0.5 to 25 parts by weight based on 100 parts by weight of rubber.

unless otherwise indicated all parts and percentages are by weight.

For use the organosilanes described above can be directly added to the rubber mixture or to the constituents of this mixture. Thereby it is not necessary and not advantageous to hydrolyze the organosilane before the addition.

However, the described organosilicon compounds can also be added to a part of the fillers, especially on the basis of their easy dosability and handling, whereby the liquid organosilane is converted into a powdery product and thus be used. In a given case, however, it is also possible, although not of special advantage, to uniformly coat the organosilane on the surface of the filler particles and in this form to carry out the use. All three or only two of the described methods of use can also be combined.

The rubber mixtures can be produced with one or more, in a given case oil-extended, natural and/or synthetic rubbers. These include especially natural rubber, synthetic rubbers, preferably diene elastomus as for example polybutadiene, polyisoprene, e.g., cis-polyisoprene, butadiene- styrene copolymer, butadiene-acrylonitrile copolymer, polymerized 2-chlorobutadiene, also butyl rubber, halogenated butyl rubber such as chlorinated butyl rubber, brominated butyl rubber as well as other known diene rubbers as for example terpolymers of ethylene, propylene and for example non-conjugated dienes and also non-conjugated polyenes, e.g., ethylene-propylene-cyclooctadiene, ethylene-propylene-norbornadiene, ethylene-propylene dicyclo-pentadiene and ethylene-propylene-cyclododecatriene. Also there can be used trans-polypentenamer, carboxy or epoxy rubbers and the like known elastomers. The chemical derivatives of natural rubber and modified natural rubber can also be used in the invention.

There can be added, in a given case, to the rubber mixtures of the organic polymers, the cross-linking system, the siliceous fillers and the organosilane additive known reaction accelerators, as well as one or more compounds of the group of antiaging agents, heat stabilizers, light stabilizers, ozone stabilizers, processing aids, plasticizers, tackifier, propellants, dyestuffs, pigments, waxes, extenders such as for example sawdusts, organic acids as for example stearic acid, benzoic acid, or salicyclic acid, additionally lead oxide or zinc oxide, activators such as for example triethanolamine, polyethylene glycol or hexanetriol-1,2,6, which are collectively known in the rubber industry. For the vulcanization the rubber mixture is generally mixed with cross-linking agents such as especially peroxides, e.g., benzoyl peroxide, sulfur or in special cases magnesium oxide, as well as in a given case vulcanization accelerators or mixtures of these.

The production of rubber mixtures as well as molding and vulcanization is carried out according to customary procedures in the rubber industry.

Industrial fields of use for the described rubber mixtures for examples are:

Industrial rubber articles such as cable insulation, hoses, driving belts, V-belts, conveyor belts, roller coating, vehicle tire treads, especially PKW and LKW-tire treads, as well as tire carcasses and tire sidewalls, cross country tires, shoe sole materials, packing rings, damping elements and many others. The new rubber mixtures have also been tested for glass fiber-adhesive mixtures and the like.

The filler Ultrasil VN2 is a precipitated active silica having a specific surface area (measured according to BET) of 130 m² /g and an average primary particle size of 28 nm.

The Ultrasil VN3 is likewise a precipitated active silica but has a specific surface area of 210 m² /g and an average primary particle size of 18 nm.

The rubber Buna CB10 is a polybutadiene rubber having a high cis-1,4- content.

Russ Corax 6LM is a ISAF-active carbon black wherein the large characters LM is an abbreviation for "Low Modulus".

Without limiting the invention the results are given in the following individual recipes for the new rubber mixtures with test results on the vulcanizates and evaluations or comparisons of these results. Therein many different concepts are repeated so that abbreviations can be used.

                                      Definitions of the Abbreviations             __________________________________________________________________________     Used                                                                           Abbreviation  Designation  Measured                                            __________________________________________________________________________     DH      Defo hardness      grams (g)                                           DE      Defo elasticity    --                                                  t.sub.5 Mooney-scorch time minutes                                             t.sub.35                                                                               Mooney-cure time   minutes                                             ML 4    Mooney plasticity at 100° C,                                            standard rotor, testing                                                        time: 4 minutes    --                                                  sp. gr. Specific gravity   g/cm.sup.3                                          VZ      Vulcanization time minutes                                             VT      Vulcanization temperature                                                                         ° C.                                         ZF      Tensile strength   kp/cm.sup.2 (kgf/cm.sup.2)                          M(300, 200)                                                                            Modulus            kp/cm.sup.2 (kgf/cm.sup.2)                          BD      Elongation at break                                                                               %                                                   bl.D.   Remaining elongation after break                                                                  %                                                   E       Rebound            %                                                   EF      Resistance to tear propagation                                                                    kp/cm (kgf/cm)                                      A       Abrasion (also "DIN abrasion")                                                                    mm.sup.3                                            ΔT                                                                               Temperature increase (see Goodrich                                             Flexometer)        ° C                                          __________________________________________________________________________

Testing Standards

The physical tests were carried out at room temperature according to the following standard specifications:

    ______________________________________                                         (DIN = German industrial standards)                                            ______________________________________                                         Tensile strength, elongation at break and                                      modulus on 6 mm large rings                                                                            DIN 53504                                              Tear Propagation resistance                                                                            DIN 53507                                              Rebound                 DIN 53512                                              Shore A hardness        DIN 53505                                              Specific gravity        DIN 53550                                              Mooney Test             DIN 53524                                              Goodrich Flexometer (Determination of the                                       heat build-up, ΔT                                                                               ASTM D 623-62                                          Abrasion                DIN 53516                                              ______________________________________                                    

The vulcanizates were always produced in a steam heated multiple die press at the stated vulcanization temperatures.

In the examples, and elsewhere unless otherwise indicated all amounts of materials are always given in parts by weight.

                  Example 1                                                        ______________________________________                                         Recipe:           Mixture 1                                                                               Mixture 2                                                                               Mixture 3                                  ______________________________________                                         Natural rubber                                                                  (Ribbed Smoked Sheets I)                                                                        100      100      100                                        Pentachlorthiophenyl-zinc                                                       salt (Renacit IV of                                                            Farbenfabriken BAYER)                                                                           0.25     0.25     0.25                                       Finely divided precipi-                                                         tated silica (Ultrasil                                                         VN 3 of Degussa) 40       40       40                                         Zinc oxide        3        3        3                                          Stearic acid      2        2        2                                          3-mercaptopropyltrimethoxy-                                                     silane           --       2        --                                         Bis-[3-trimethoxysilyl-                                                        trisulfide        --       --       2                                          Dibenzothiazyldisulfide                                                                          0.8      0.8      0.8                                        Diphenylguanidine 2.25     2.25     2.25                                       Sulfur            2.5      2.5      2.5                                        ______________________________________                                    

Mixing Procedure

Preliminary mixing was in a kneader at 80° C. flow temperature

    ______________________________________                                         Additive or Treatment                                                                               Ended After                                               ______________________________________                                         Natural rubber       0 minutes                                                 1/2 the amount of silica                                                       stearic acid         1 minute                                                  1/2 the amount of silica                                                       zinc oxide and organosilane                                                                         2.5 minutes                                               Ram lifted and swept down                                                                           4 minutes                                                 Batch dumped         4.5 minutes                                               ______________________________________                                    

This mixture was allowed to be stored for 24 hours. Then the final mixing took place in the kneader at 80° C. flow temperature (Mixing Time 1.5 minutes).

    ______________________________________                                         Properties of the unvulcanized mixtures                                               Mixture 1 Mixture 2   Mixture 3                                         ______________________________________                                         DH/DE    675/20      precured    650/20                                                             (scorched)                                                t.sub.5  6.4         --          5.0                                           t.sub.35 7.5         --          5.8                                           ML 4     57          232         54                                                                 (increasing)                                              sp.gr.   1.13        1.13        1.13                                          ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized Mixture                                           Vulcanization temperature: 150° C.                                      Mixture                                                                               VZ     ZF     M 300 BD   bl.D E   SH  EF   A                            ______________________________________                                         1      10     256    62    622  41   50  62  39                                       20     250    58    630  43   47  64  31                                       40     229    48    640  37   46  62  35   165                                 60     227    42    678  33   45  62  35                                2      10                                                                             20                                                                             40                                                                             60                                                                      3      10     274    95    558  41   47  63  27                                       20     257    94    548  36   48  64  29                                       40     262    84    580  35   48  61  25   140                                 60     242    76    582  28   47  61  27                                ______________________________________                                    

                  Example 2                                                        ______________________________________                                         Recipe:           Mixture 1                                                                               Mixture 2                                                                               Mixture 3                                  ______________________________________                                         cis-1,4-Polyisoprene                                                           rubber            100      100      100                                        finely divided, precipitated                                                   silica (ULTRASIL VN 3 of                                                       DEGUSSA)          50       50       50                                         Plasticizer (naphthenic                                                        hydrocarbons)     3        3        3                                          Zinc oxide (active)                                                                              2        2        2                                          Antioxidant (Mixture of                                                        aralkylated Phenols)                                                                             1        1        1                                          Mixture of equal parts of                                                      finely divided precipitated                                                    silica and hexanetriol                                                         (Aktivator R of DEGUSSA)                                                                         4        4        4                                          Benzoic acid      0.8      0.8      0.8                                        3-Mercaptopropyl-                                                              trimethoxysilane  --       1.5      --                                         Bis-[3-triethoxysilyl-                                                         propyl]-tetrasulfide                                                                             --       --       1.5                                        Dibenzothiazyldisulfide                                                                          0.8      0.8      0.8                                        Diphenylguanidine 1.6      1.6      1.6                                        Sulfur            2.5      2.5      2.5                                        ______________________________________                                    

Mixing Procedure

Premixing in a kneader at 80° C. flow temperature.

    ______________________________________                                         Additive or Treatment                                                                               Ended After                                               ______________________________________                                         cis-1.4-Polyisoprene rubber                                                                         0 minutes                                                 1/2 amount of silica, stearic acid                                                                  1 minute                                                  1/2 amount of silica, plasticizer,                                             zinc oxide, organosilane                                                                            2.5 minutes                                               Ram lifted and swept down                                                                           4 minutes                                                 Batch dumped         4.5 minutes                                               ______________________________________                                    

After standing for 24 hours final mixing was accomplished at 80° C. flow temperature in a kneader. (Mixing time 1.5 minutes).

    ______________________________________                                         Properties of the unvulcanized mixtures                                               Mixture 1 Mixture 2   Mixture 3                                         ______________________________________                                         DH/DE    1500/6.0    scorched    1375/7.0                                      t.sub.5  9.2         --          6.5                                           t.sub.35 11.6        --          8.4                                           ML 4     100         154         91                                                                 (increasing)                                              sp.gr.   1.13        1.14        1.14                                          ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized Mixture                                           Vulcanization temperature: 134° C.                                      Mixture                                                                               VZ     ZF     M 300 BD   bl.D E   SH EF    A                            ______________________________________                                         1      10     136    21    707  17   33  48  20                                       20     198    27    742  24   36  59  30   196                                 30     215    31    733  30   36  61  28                                       40     220    34    723  34   38  61  23                                2      10                                                                             20                                                                             30                                                                             40                                                                      3      10     199    47    632  23   40  63  40                                       20     242    63    640  31   42  68  44   158                                 30     266    79    628  36   43  71  41                                       40     272    87    620  41   44  72  43                                ______________________________________                                    

In examples 1 and 2 there were used a rubber mixture based on natural rubber or synthetic cis-1,4-polyisoprene which contained as the siliceous filler a precipitated finely divided silica (Ultrasil VN 3 of Degussa). As reinforcing additive for the rubber mixture there were employed bis-[3-trimethoxysilyl propyl]-trisulfide or bis-[3-triethoxysilyl propyl]-tetrasulfide and 3-mercaptopropyl trimethoxysilane was employed as a comparison material of the prior art. As is already shown by the properties of the unvulcanized mixture in producing mixtures in the internal mixer only the raw rubber mixtures of the invention are able to be worked up further while the comparison mixtures could not be further worked because of the premature scorching.

The polysulfide organosilanes of the invention only shorten the scorching time t₅ and t₃₅ a short time in the mixtures and do not negatively effect the Mooney plasticity (ML 4) as well as the ratio DH/DE, if the mixtures with the organosilane additives are compared with the standard or reference mixtures.

The vulcanization properties of the new rubber mixtures are, compared to the silane free standard mixtures, are somewhat better in their resistance and clearly superior in regards to 300 Modulus, whereby the reinforcing effect which is produced by the invention is proven by numerical data. The named important advantages were produced by means of the added organosilane.

Mixture 3 of example 2 additionally also shows extraordinarily high tear propagation resistance values (tear propagation resistance).

                  Example 3                                                        ______________________________________                                         Recipe:           Mixture 1                                                                               Mixture 2                                                                               Mixture 3                                  ______________________________________                                         Styrene-Butadiene-rubber                                                       (Buna Huls 1502)  100      100      100                                        Aluminumsilicate, precipita-                                                   ted (SILTEG AS 7 of DEGUSSA)                                                                     40       40       40                                         Zinc oxide (active)                                                                              3        3        3                                          Stearic acid      1        1        1                                          Cumaron resin (B 1/2 85° C.)                                                              5        5        5                                          Mixture of equal parts of                                                      finely divided precipitated                                                    {silica and hexanetriol                                                        {(Activator R of DEGUSSA)                                                                        5        5        5                                          {Antioxidant (Mixture of                                                       {aralkylated phenols)                                                                            1        1        1                                          3-Mercaptopropyl-                                                              trimethoxysilane  --       1.5      --                                         Bis-[3-triethoxysilyl-                                                         propyl]-tetrasulfide                                                                             --       --       1.5                                        Benzothiazyl-2-cyclo-                                                          hexylsulfenamide  0.4      0.4      0.4                                        Diphenylguanidine 0.8      0.8      0.8                                        Sulfur            2.0      2.0      2.0                                        ______________________________________                                    

Mixing Procedure

Premixing in a kneader at 80° C. flow temperature.

    ______________________________________                                         Additive or Treatment    Ended after                                           ______________________________________                                         Polymer (SBR)            0 minutes                                             1/2 amount of aluminum silicate,                                               stearic acid, antioxidant                                                                               1 minute                                              1/2 amount of aluminum silicate,                                               plasticizer, zinc oxide, organosilane,                                         remaining chemicals      2.5 minutes                                           Ram lifted and swept down                                                                               4 minutes                                             Batch dumped             4.5 minutes                                           ______________________________________                                    

Accelerator and sulfur were mixed in on the rolls (Mixing time 1.5 minutes).

    ______________________________________                                         Properties of the unvulcanized mixtures                                               Mixture 1 Mixture 2   Mixture 3                                         ______________________________________                                         t.sub.5  4.9         --          3.1                                           t.sub.35 5.9         --          4.3                                           ML 4     78          196         82                                                                 (increasing)                                              sp. gr.  1.16        1.16        1.16                                          ______________________________________                                    

    ______________________________________                                         Properties of vulcanized mixtures                                              Vulcanization temperature: 150° C.                                      Mixture                                                                               VZ     ZF     M 300 BD   bl.D E   SH   EF  A                            ______________________________________                                         1       8     127    39    610  19   47  58   5                                       10     140    40    630  21   47  58   4                                       15     146    41    690  18   47  58   5   160                                 20     121    41    583  16   47  58   4                                2       8                                                                             10                                                                             15                                                                             20                                                                      3       8     142    78    560  15   50  59   6                                       10     140    69    528  13   50  59   5                                       15     130    71    465  11   51  60   4   132                                 20     121    72    500  13   51  60   5                                ______________________________________                                    

                  Example 4                                                        ______________________________________                                         Recipe:           Mixture 1                                                                               Mixture 2                                                                               Mixture 3                                  ______________________________________                                         Styrene-Butadiene-rubber                                                       (Buna Huls 1502)  100      100      100                                        Finely divided, precipitated                                                   silica (ULTRASIL VN 3 of                                                       DEGUSSA)          50       50       50                                         Zinc oxide (active)                                                                              1        1        1                                          Stearic acid      2        2        2                                          Antioxidant (mixture of                                                        aralkylated phenols)                                                                             1        1        1                                          Polyethylene glycol, molecular                                                 wt. 4000 (PEG 4000)                                                                              2        2        2                                          3-mercaptopropyl-                                                              trimethoxysilane  --       2        --                                         Bis-[3-trimethoxysilyl-                                                        propyl]-disulfide --       --       2                                          Dibenzothiazyldisulfide                                                                          1        1        1                                          Diphenylguanidine 2        2        2                                          Sulfur            2        2        2                                          ______________________________________                                    

Mixing Procedure

Premixing in a kneader at 80° C. flow temperature.

    ______________________________________                                         Additive or Treatment    Ended After                                           ______________________________________                                         Polymer (SBR)            0 minutes                                             1/2 amount of silica, stearic acid,                                            antioxidant              1 minute                                              1/2 amount of silica, zinc oxide,                                              organosilane, other      2.5 minutes                                           Ram lifted and swept down                                                                               4 minutes                                             Batch dumped             4.5 minutes                                           ______________________________________                                    

After 24 hours storage the mixing in the kneader at 80° C flow through temperature was completed (Mixing time 1.5 minutes).

    ______________________________________                                         Properties of the unvulcanized mixtures                                               Mixture 1 Mixture 2   Mixture 3                                         ______________________________________                                         DH/DE    2250/19.5   scorched    2050/31.0                                     t.sub.5  8.1         --          7.8                                           t.sub.35 10.0        --          9.6                                           ML 4     143         242         116                                                                (increasing)                                              sp. gr.  1.16        1.16        1.17                                          ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized mixtures                                          Vulcanization temperature: 150° C.                                      Mixture                                                                               VZ     ZF     M 300 BD   bl.D E   SH  EF   A                            ______________________________________                                         1       5     170    40    660  40   33  71  17                                       10     174    42    640  34   33  72  14                                       15     178    41    625  31   33  71  13   126                                 20     196    42    647  32   33  71  14                                2       5                                                                             10                                                                             15                                                                             20                                                                      3       5     208    63    592  33   32  70  17                                       10     222    77    548  29   32  71  13                                       15     222    85    523  24   32  70  14    89                                 20     216    85    513  21   32  71  13                                ______________________________________                                    

                  Example 5                                                        ______________________________________                                         Recipe:           Mixture 1                                                                               Mixture 2                                                                               Mixture 3                                  ______________________________________                                         Styrene-Butadiene-rubber                                                       (Buna Huls 1500)  100      100      100                                        Colloidalkaolin   75       75       75                                         Zinc oxide        4        4        4                                          Stearic acid      2        2        2                                          3-mercaptopropyl-                                                              trimethoxysilane  --       2.5      --                                         Bis-[3-triethoxysilyl-                                                         propyl]-tetrasulfide                                                                             --       --       2.5                                        Dibenzothiazyldisulfide                                                                          1.2      1.2      1.2                                        Diphenylguanidine 1.2      1.2      1.2                                        Sulfur            2.75     2.75     2.75                                       ______________________________________                                    

Mixing Procedure

Premixing in a kneader at 80° C. flow temperature.

    ______________________________________                                         Additive or Treatment                                                                               Ended After                                               ______________________________________                                         Rubber               0 minutes                                                 1/2 amount of Kaolin, zinc oxide,                                              organosilane         2.5 minutes                                               Ram lifted and swept down                                                                           4 minutes                                                 Batch dumped         4.5 minutes                                               ______________________________________                                    

After 24 hours storage the mixing in the kneader at 80° C. flow through temperature was completed (Mixing time 1.5 minutes).

    ______________________________________                                         Properties of the unvulcanized mixtures                                               Mixture 1 Mixture 2   Mixture 3                                         ______________________________________                                         DH/DE    1750/27     2550/32.5   1450/23.5                                     t.sub.5  34.0        6.6         29.2                                          t.sub.35 41.3        11.6        38.2                                          ML 4     63          80          61                                            sp. gr.  1.32        1.32        1.32                                          ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized mixtures                                          Vulcanization temperature: 150° C.                                      Mixture                                                                               VZ     ZF     M 300 BD   bl.D.                                                                               E   SH  EF   A                            ______________________________________                                         1      15     101     50   635  53   45  64  13                                       30      99     66   483  36   42  67   6                                       45      96     65   490  34   40  66   6   268                                 60      94     64   480  34   40  67   9                                2      15     154    137   335  18   45  67   8                                       30     146    138   307  13   44  68   5                                       45     145    138   305  10   43  68   5   210                                 60     147    143   303  11   42  67   5                                                     M 200                                                     3      15     125     77   440  22   42  66   8                                       30     125    101   287  14   41  69   5                                       45     125    102   262  10   40  69   5   223                                 60     129    104   293  14   39  69   4                                ______________________________________                                    

In examples 3 to 5 there were used rubber mixtures based on styrene-butadiene copolymers which contained as silicious fillers synthetic aluminum silicate or precipitated silica or a natural silicate (colloidal kaolin). As organosilane reinforcing additives there were employed bis-[3-triethoxysilyl propyl]-tetrasulfide or bis-[3-trimethoxysilyl propyl]-disulfide; these were compared with the 3-mercaptopropyl trimethoxysilane of the prior art in otherwise identical mixtures.

According to examples 3 and 4 it was not possible to produce kneader mixtures with 3-mercaptopropyl trimethoxysilane without premature scorching while this presents no problem with the rubber mixtures containing the polysulfideorganosilanes of the invention.

In comparison with the respective standard mixtures without silane additive the vulcanization properties of the new rubber mixtures are clearly better. Tensile strength and modulus are increased, the remaining elongation after break was reduced and the DIN abrasion improved.

Example 5 shows that this effect occurs even in the addition of a relatively inactive silicate filler such as colloidal kaolin.

Example 5 also demonstrates with reference to the properties of the unvulcanized mixtures the clear advance of the present invention over the prior art compound 3-mercaptopropyl trimethoxysilane in that the prior art compound increases the values for DH/DE and ML 4 and it drastically shortens the scorch time t₅. On the contrary in the new rubber mixtures the values DH/DE and ML 4 are changed in a positive direction while the Mooney-scorch time t₅ is not substantially different from that of the comparison mixture without any silane additive.

The following examples 6 to 9 illustrate the fact that the new rubber mixtures also can be produced with equally good success based on butadiene acrylonitrile copolymers, butyl rubber, polychloroprene rubber or ethylenepropylene-terpolymer.

                  Example 6                                                        ______________________________________                                         Recipe:                Mixture 1                                                                               Mixture 2                                      ______________________________________                                         Butadiene-acrylonitrile-rubber                                                 (Perbunan N 3310 of Farbenfabriken                                             Bayer AG)              100      100                                            Pyrogenic silica (Aerosil 130 V                                                of DEGUSSA             40       40                                             Zinc oxide             4        4                                              Bis-[3-triethoxysilyl-propyl]                                                  tetrasulfide           --       1.5                                            Dibenzothiazyldisulfide                                                                               1.5      1.5                                            Diphenylguanidine      1.5      1.5                                            Sulfur                 2.75     2.75                                           ______________________________________                                    

Mixing Procedure

Premixing in a kneader at 80° C. flow temperature.

    ______________________________________                                         Additive or Treatment                                                                               Ended After                                               ______________________________________                                         Butadiene-acrylonitrile-rubber                                                                      0 minutes                                                 1/2 amount of silica, stearic acid                                                                  1 minute                                                  1/2 amount of silica, zinc oxide,                                              organosilane         2.5 minutes                                               Ram lifted and swept down                                                                           4 minutes                                                 Batch dumped         4.5 minutes                                               ______________________________________                                    

After 24 hours storage the mixing in the kneader at 80° C. flow through temperature was completed (Mixing time 1.5).

    ______________________________________                                         Properties of the unvulcanized mixtures                                                       Mixture 1 Mixture 2                                             ______________________________________                                         DH/DE            2350/26     1950/31                                           t.sub.5          10.6        7.8                                               t.sub.35         13.4        9.8                                               ML 4             132         105                                               sp. gr.          1.21        1.21                                              ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized mixtures                                          Vulcanization temperature: 150° C.                                      Mixture                                                                               VZ     ZF     M 200 BD   bl.D.                                                                               E   SH  EF   A                            ______________________________________                                         1       60    182     99   303  3    18  76  12                                        80    178    110   285  3    17  77  10   107                                 100    161    106   265  2    17  76  12                                       120    158    109   262  1    17  79  13                                2       60    200    179   218  1    16  78   7                                        80    210    189   215  1    16  78   9    58                                 100    226    187   215  1    16  77   9                                       120    228    204   225  2    16  78   8                                ______________________________________                                    

                  Example 7                                                        ______________________________________                                         Recipe:                Mixture 1                                                                               Mixture 2                                      ______________________________________                                         Butyl rubber           100      100                                            Finely divided, precipitated                                                   silica (ULTRASIL VN 3 of Degussa)                                                                     50       50                                             Zinc oxide             5        5                                              Stearic acid           1        1                                              Plasticizer (Petroleum oil)                                                                           5        5                                              Bis-[3-triethoxysilyl-propyl]-                                                 tetrasulfide           --       1.5                                            2-Mercaptobenzothiazole                                                                               1        1                                              Tetramethylthiuramdisulfide                                                                           0.5      0.5                                            Sulfur                 1.5      1.5                                            ______________________________________                                    

Mixing Procedure

Premixing in the kneader at 60° C flow temperature.

    ______________________________________                                         Additive or Treatment                                                                               Ended After                                               ______________________________________                                         Butyl rubber         0 minutes                                                 1/2 amount of silica, stearic acid                                                                  2 minutes                                                 1/2 amount of silica, zinc oxide,                                              organosilane, plasticizer                                                                           4 minutes                                                 Ram lifted and swept down                                                                           6 minutes                                                 Batch dumped         7 minutes                                                 ______________________________________                                    

The final mixing took place on a open mill at 50° C. roll temperature.

    ______________________________________                                         Additive or Treatment                                                                               Ended After                                               ______________________________________                                         Batch charged        0 minutes                                                 Cut in twice right and left                                                                         1 minute                                                  Accelerator and sulfur                                                                              2 minutes                                                 Cut in twice right and left                                                                         4 minutes                                                 Mixture sheet pulled off                                                                            5 minutes                                                 ______________________________________                                    

    ______________________________________                                         Properties of the unvulcanized mixtures                                                       Mixture 1 Mixture 2                                             ______________________________________                                         DH/DE            4300/3      3200/5                                            t.sub.5          1.2         2.9                                               t.sub.35         40          17.6                                              ML 4             135         112                                               sp. gr.          1.15        1.15                                              ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized mixtures                                          Vulcanization temperature: 160° C.                                      Mixture                                                                               VZ     ZF     M 300 BD   bl.D.                                                                               E   SH  EF   A                            ______________________________________                                         1      10      85    19    893  100  12  64  15                                       20     103    23    850  100  13  67  16                                       40     117    27    818  100  13  68  23                                       60     116    28    795  96   13  70  25   270                                 80     112    28    778  93   13  70  26                                2      10     108    27    805  97   11  63  17                                       20     133    34    773  78   11  64  22                                       40     145    40    738  68   12  67  23                                       60     148    43    708  64   12  69  28   227                                 80     151    45    693  63   12  69  27                                ______________________________________                                    

                  Example 8                                                        ______________________________________                                         Recipe:                Mixture 1                                                                               Mixture 2                                      ______________________________________                                         Polychlorobutadiene rubber                                                                            100      100                                            (Baypren 210 of Farbenfabriken                                                 Bayer AG, Leverkusen)                                                          Di-o-tolylguanidine    0.5      0.5                                            Magnesiumoxide         4        4                                              Stearic acid           1        1                                              Mixture of liquid and plastic                                                  paraffins (Vaseline)   1        1                                              Phenyl-β-naphthylamine (anti-                                             oxidant)               2        2                                              Finely divided, precipitated                                                   silica (ULTRASIL VN 2 of DEGUSSA)                                                                     50       50                                             Plasticizer                                                                    (naphthenic hydrocarbons)                                                                             10       10                                             Bis-[3-triethoxysilyl-propyl]-                                                 tetrasulfide           --       1.5                                            2-mercaptoimidazoline  0.75     0.75                                           Zinc oxide             5        5                                              ______________________________________                                    

Mixing Procedure:

Premixing in the kneader at 60° C. flow temperature.

    ______________________________________                                         Additive or Treatment    Ended After                                           ______________________________________                                         Polychlorobutadiene, guanidine derivate                                                                 0 minutes                                             Antioxidant, magnesium oxide                                                   Stearic acid, vaceline, 1/3 of the amount                                                               1 minute                                              of the silica                                                                  1/3 of the amount of the silica, 1/2 the                                       amount of the plasticizer, organosilane                                                                 2.5 minutes                                           1/3 the amount of the silica, 1/2 the                                          amount of the plasticizer                                                      Ram lifted and swept down                                                                               4 minutes                                             Removal and cooling 5 minutes in a waterbath                                                            5 minutes                                             ______________________________________                                    

After 24 hours storage there was mixed in the kneader at 60° C flow temperature the 2-Merkaptoimidazoline and the zinc oxide and there was 5 minutes cooling in the waterbath.

    ______________________________________                                         Properties of the unvulcanized mixtures                                                       Mixture 1 Mixture 2                                             ______________________________________                                         DH/DE                                                                          t.sub.5          6.2         5.5                                               t.sub.35         10.8        10.1                                              ML 4             91          84                                                sp. gr.          1.42        1.42                                              ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized mixtures                                          Vulcanization temperature: 150° C.                                      Mixture                                                                               VZ     ZF     M 300 BD   bl.D.                                                                               E   SH  EF   A                            ______________________________________                                         1      10     156    47    810  28   34  57  37                                       20     167    52    790  18   33  61  31                                       30     171    53    742  17   33  62  23   161                                 40     171    53    735  15   33  62  19                                2      10     196    75    673  17   37  60  29                                       20     208    105   555  10   36  63  14                                       30     214    113   532  10   35  64  11   105                                 40     216    119   513  10   35  65  14                                ______________________________________                                    

                  Example 9                                                        ______________________________________                                         Recipe:                Mixture 1                                                                               Mixture 2                                      ______________________________________                                         Terpolymer ethylene-propylene-                                                 rubber (Keltan 70 of DSM)                                                                             100      100                                            Finely divided, precipitated                                                   silica (EXTRUSIL of DEGUSSA)                                                                          100      100                                            Naphthenic hydrocarbon as                                                      plasticizer            50       50                                             Titandioxide           10       10                                             Zinc oxide             5        5                                              Stearic acid           1        1                                              Bis-[3-triethoxysilyl-propyl]-                                                 tetrasulfide           --       5                                              Tetramethylthiuramidisulfide                                                                          0.8      0.8                                            Dimethyldiphenylthiuramdisulfide                                                                      1.5      1.5                                            Telluriumdiethyldithiocarbamate                                                                       0.8      0.8                                            Dipentamethylenethiuramtetrasulfide                                                                   0.8      0.8                                            Sulfur                 2.0      2.0                                            ______________________________________                                    

Mixing Procedure

Premixing in the kneader at 80° C. flow temperature.

    ______________________________________                                         Additive or Treatment                                                                               Ended After                                               ______________________________________                                         Ethylene-Propylene-Terpolymer                                                                       0 minutes                                                 1/2 amount of the silica, stearic acid                                                              1 minute                                                  1/2 amount of the silica, zinc oxide                                           organosilane, remaining chemicals                                                                   2.5 minutes                                               Ram lifted and swept down                                                                           4 minutes                                                 Batch dumped         5 minutes                                                 ______________________________________                                    

After 24 hours storage the mixing was finished in the kneader at 80° C. flow temperature (Mixing time 1.5 minutes).

    ______________________________________                                         Properties of the unvulcanized mixtures                                                       Mixture 1 Mixture 2                                             ______________________________________                                         DH/DE            550/17.5    400/19.5                                          t.sub.5          8.5         19.2                                              t.sub.35         16.4        50.4                                              ML 4             50          40                                                sp. gr.          1.16        1.16                                              ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized mixtures                                          Vaulcanization temperature: 160° C.                                     Mixture                                                                               VZ     ZF     M 300 BD    bl.D.                                                                               E    SH   EF                             ______________________________________                                         1      10     67     23    825   43   40   53   7                                     20     62     29    627   25   42   57   3                                     30     55     32    550   21   42   59   2                              2      10     77     42    725   26   41   54   8                                     20     91     74    392    7   43   60   3                                     30     98     98    300    5   44   63   2                              ______________________________________                                    

In example 6 there was used a rubber mixture formulated according to the invention based on a nitrile rubber which contained as the siliceous filler a pure silica produced by flame hydrolysis (Aerosil 130V of Degussa) and to which was added bis-[3-triethoxysilyl-propyl]-tetrasulfide as the organosilane reinforcing additive.

The Mooney viscosity of mixture 2 of Example 6 is clearly reduced in comparison to the standard mixture without organosilane addition. This signifies a reduced expenditure of energy and a lower cost in the further working of the raw mixture; the scorching time t₅ is only shortened unsubstantially. The vulcanizate of Mixture 2 shows a significant improvement in regard to tensile strength, modulus and DIN-abrasion when it is compared with comparison mixture 1 without organosilane addition.

According to example 7 the rubber mixture of the invention was based on butyl rubber containing a precipitated silica (Ultrasil VN 3 of Degussa) as the siliceous filler and the bis-[3-triethoxy-silyl propyl]-tetrasulfide as the organosilane reinforcing additive.

This addition of organosilane did not lead to premature scorching of the already very sharply accelerated standard mixture, but instead surprisingly to an increase in the Mooney-scorch time t₅. Tensile strength, modulus and remaining elongation of the vulcanizate were clearly better in comparison to the vulcanizate from the standard mixture.

Example 8 describes a rubber mixture based on a polychloroprene rubber with a precipitated silica (Ultrasil VN 3 of Degussa) as the siliceous filler and again using the bis-[3-triethoxysilyl propyl]-tetrasulfide as the organosilane reinforcer for cross-linking. The scorching behaviour of Mixture 2 is practically unchanged in comparison to the standard mixture, in regard to the Mooney viscosity Mixture 2 behaves somewhat more favourably. The properties of the vulcanizate of the rubber composition of the invention compared to those of the standard mixture are clearly superior. The tensile strength is more than 40 kp/cm² (40 kgf/cm²) and the 300% modulus at the same time more than 60 kp/cm² higher. The latter indicates an improvement of about 100% or more based on the Mixture 1 devoid of the organosilane.

Example 9 concerns a rubber mixture based on an ethylene-propylene nonconjugated diene-terpolymer with a further precipitated silica (Extrusil of Degussa) as the siliceous filler and the bis-[3-triethoxysilyl propyl]-tetrasulfide as the organosilane. Also in this case there is produced a surprising increase in the scorch time t₅ ; ML 4 is reduced about 10 Mooney units, both in comparison to the standard mixture without organosilane. The properties of the vulcanizate from Mixture 2 formulated according to the invention clearly exceed those of Mixture 1 without silane in regard to tensile strength, modulus and remaining elongation after break.

                  Example 10                                                       ______________________________________                                         Passenger automobile - tire tread mixture                                      Recipe                 Mixture 1                                                                               Mixture 2                                      ______________________________________                                         Oil extended styrene-                                                          butadiene rubber                                                               (Buna Huls 1712)       96.5     96.5                                           cis-1,4-Polybutadiene -(Buna CB 10)                                                                   30       30                                             Finely divided precipitated                                                    silica (ULTRASIL VN 3 of DEGUSSA)                                                                     75       70                                             Bis-[3-triethoxysilyl-propyl]-                                                 tetrasulfide           5        --                                             Mixture of equal parts of                                                      precipitated silica (ULTRASIL VN 3)                                            and Bis-[3-triethoxysilyl-propyl]-                                             tetrasulfide           --       10                                             Zinc oxide             4        4                                              Stearic acid           1.2      1.2                                            Plasticizer (naphthenic                                                        hydrocarbons)          15       15                                             Antioxidant, phenyl-β-naphthyl-                                           amine                  1.5      1.5                                            Antioxidant, N-Iso-propyl-N-'-                                                 phenyl-p-phenylene-diamine                                                                            1.5      1.5                                            Benzthiazolyl-2-cyclohexylsul-                                                 fenamide               1.2      1.2                                            Diphenylguanidine      3.5      3.5                                            Sulfur                 1.6      1.6                                            ______________________________________                                    

Mixing Procedure: "Up-side-down"

Premixing in the Kneader at 80° C. flow temperature

    ______________________________________                                         Additive or Treatment    Ended-After                                           ______________________________________                                         Step 1                                                                         Fillers, chemicals, polymers                                                                            0 minutes                                             Ram lifted and swept down                                                                               3 minutes                                             Batch dumped             3.5 minutes                                           Storage                  24 hours                                              Step 2                                                                         Final mixing in the kneader at 80° C flow temperature.                  Accelerator and sulfur are mixed in in the kneader                             Mixing time              1.5 minutes                                           ______________________________________                                    

    ______________________________________                                         Properties of the unvulcanized mixtures                                                       Mixture 1 Mixture 2                                             ______________________________________                                         t.sub.5          20.0        18.1                                              t.sub.35         26.5        26.0                                              ML 4             67          67                                                sp. gr.          1.19        1.19                                              ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized mixtures                                          Vulcanization temperature: 160° C.                                      Mixture                                                                               VZ     ZF     M 300 BD   bl.D.                                                                               E   SH   EF  A                            ______________________________________                                         1      20     190    66    592  26   38  64   23  91                           2      20     196    63    627  26   38  62   27  90                           ______________________________________                                    

                  Example 11                                                       ______________________________________                                         Tire tread mixture                                                             Recipe:                Mixture 1                                                                               Mixture 2                                      ______________________________________                                         Natural rubber                                                                 (Ribbed Smoked Sheets I)                                                                              100      100                                            Pentachlorthiophenyl-zinc salt                                                 (Renacit IV of Farben-                                                         fabriken Bayer, Leverkusen)                                                                           0.25     0.25                                           ISAF-LM Carbon black                                                           (CORAX 6 LM of Degussa)                                                                               60       --                                             Mixture of 10 parts of bis[3-                                                  triethoxysilyl-propyl]-tetra-                                                  sulfide and 100 parts of                                                       precipitated silica (ULTRASIL                                                  VN 3 of Degussa)       --       66                                             Zinc oxide             5        5                                              Stearic acid           2.5      2.5                                            Antioxidant, phenyl-α-                                                   naphthylamine          1        1                                              Antioxidant phenyl-β-                                                     naphthylamine          1        1                                              Antioxidant N-Isopropyl-                                                       N-phenyl-p-phenylendiamine                                                                            0.8      0.8                                            Rubber-ocozerite (Protektor 3888                                               of Luneburge Wachs-                                                            bleiche, GmbH)         0.8      0.8                                            Plasticizer (naphthenic                                                        hydrocarbon)           2        2                                              Bis-[2-ethylamino-4-diethylamino-                                              6-triazinyl]-disulfide 0.6      0.6                                            Diphenylguanidine      --       2                                              Sulfur                 1.2      1.2                                            ______________________________________                                    

Mixing Procedure:"Up-side-down"

Premixing in the kneader at 80° C. flow temperature

    ______________________________________                                         Additive or Treatment                                                                               Ended After                                               ______________________________________                                         Step 1:                                                                        Fillers, chemicals, polymer                                                                         0 minutes                                                 Ram lifted and swept down                                                                           3 minutes                                                 Batch dumped         3.5 minutes                                               Storage time         24 hours                                                  Step 2:                                                                        Final mixing in the kneader at 80° C. flow temperature.                 Accelerator and sulfur are mixed in in the kneader                             Mixing time          1.5 minutes                                               ______________________________________                                    

    ______________________________________                                         Properties of the unvulcanized mixtures                                                       Mixture 1 Mixture 2                                             ______________________________________                                         Mooney Scorch t.sub.5                                                                           25.4        19.9                                              Mooney Cure t.sub.35                                                                            28.1        25.3                                              Mooney Viscosity ML 4                                                                           88          77                                                sp.gr.           1.15        1.18                                              ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized mixtures                                          Vulcanization temperature: 145° C.                                      Mix-                                           T                               ture VZ     ZF     M 300 BD   E   SH  EF  A    (0.250")                        ______________________________________                                         1    60     249    139   490  36  68  31  102  87                              2    60     257    119   547  41  76  42  104  64                              ______________________________________                                    

According to Example 10 a passenger automobile tire tread (PKW) recipe and according to Example 11 an earth mover tire tread recipe are disclosed and used. As reinforcing additive for both recipes there were used bis-[3-triethoxysilylpropyl]-tetrasulfide, for the PKW tire tread in the form of a mixture with silica in the ratio 1:1 and for the earth mover tire tread in the form of a mixture with finely divided silica in the ratio 1:10.

Example 10 shows that the range of error of the rubber technique investigating methods used there was no difference between the application of the reinforcing additive in pure form and the application of the reinforcing additive in the form of a mixture with precipitated highly dispersed silica.

The properties of the unvulcanized and the vulcanized mixtures show one skilled in the art that by using the reinforcing additive of the invention there are imparted to a great extent to the silica reinforced PKW tire tread mixtures properties which correspond to the properties of corresponding carbon black mixture.

Also, for the first time, it is possible by use of the polysulfide functional organosilane reinforcing additive to produce silica reinforced PKW tire tread mixtures without change of the previously customary mixing and vulcanization processes in the rubber industry, which mixtures in all industrial applications have characteristics which are at least equal to corresponding carbon black reinforced mixtures.

In Example 11 the reinforcing additive of the invention in a silica reinforced Earth-Mover tire tread mixture is compared with a conventional carbon black reinforced Earth-Mover tire tread mixture.

In Example 11 it is proven that by using the additives of the invention there are imparted such properties to silica reinforced rubber mixture which in decisive points exceed those of carbon black reinforced mixtures; for example in regard to tear propagation resistance and the heat build up (Heat build-up Goodrich Flexometer Test).

In comparison to the standard Mixture 1 it is established that by use of the reinforcing additive of the invention the Mooney-scorch and Mooney cure time are somewhat shortened but they still remain in a range suitable for industrial practice. The raw mixture viscosity is 11 Mooney units lower in the composition of the invention in comparison to the standard mixture which is a altogether a desired effect since it leads f.i. to a reduction in the production costs for the tire manufacturer.

In the vulcanization properties which in general correspond to those of the standard mixture there are two properties in which the mixture of the invention stands out; the clearly increased resistance to tear propagation and the reduced heat build up. The resistance to tear propagation is increased 35% in comparison to the carbon black reinforced standard (or reference) mixture, the heat build up is lowered about 31%, from 87° C. to 64° C. In the evaluation of the absolute values of the Goodrich Flexometer test it should be observed that this was measured with a stroke of 0.250 inch, while ASTM prescribes a stroke of 0.175 inch. It is especially noteworthy that the DIN abrasions of the carbon black mixture and of the silica mixture are practically the same.

It was also again confirmed that by use of the organosilane reinforcing additive of the invention that for the first time it is possible to easily produce practical mixtures with only silica or siliceous filler and then to vulcanize which products in the sum of their properties are equal to corresponding carbon black filled mixtures and even exceed the carbon black mixtures in decisive characteristics.

The rubbers disclosed above are all curable, e.g., with sulfur or other curing (vulcanizing) agents.

The compositions of the invention can consist of or consist essentially of the siliceous filler and the organosilane or the composition can consist of or consist essentially of these components with the other materials mentioned.

                  EXAMPLE 12                                                       ______________________________________                                         Passenger Car Tire Tread Mixture                                               Recipe                 Mixture 1                                                                               Mixture 2                                      ______________________________________                                         Oil extended styrene-                                                          butadiene rubber                                                               (Buna Huls 1712)       96.5     96.5                                           cis-1,4-Polybutadiene                                                          (Buna CB 10)           30       30                                             Carbon Black ISAF                                                              (Corax 6 of DEGUSSA)   75       37.5                                           Finely divided precipitated                                                    silica (ULTRASIL VN 3 of DEGUSSA)                                                                     --       35                                             Mixture of equal parts of precipi-                                             tated silica (ULTRASIL VN 3) and                                               Bis-[3-triethoxysilyl-propyl]-                                                 tetrasulfide           --       5                                              Zinc oxide             4        4                                              Stearic acid           1.2      1.2                                            Plasticizer (highly                                                            aromatic hydrocarbons  15       15                                             Antiager (N-Iso-propyl-N'-                                                     phenyl-p-phenylene-diamine)                                                                           1.5      1.5                                            Antioxidant (Phenyl-β-naphthyl-                                           amine)                 1.5      1.5                                            Benzothiazolyl-2-cyclohexylsul-                                                fenamide               1.2      1.2                                            Diphenylguanidine      --       1.5                                            Sulfur                 1.6      1.6                                            ______________________________________                                    

Mixing Procedure: "Up-side-down"

Premixing in a kneader at 80° C. flow temperature

    ______________________________________                                         Additive or Treatment                                                                               Ended-After                                               ______________________________________                                         Step 1                                                                         Fillers, chemicals, polymers                                                                        0 minutes                                                 Ram lifted and swept down                                                                           3 minutes                                                 Batch dumped         3.5 minutes                                               Storage              24 hours                                                  ______________________________________                                    

Step 2

Final mixing in the kneader at 80° C. flow temperature. Accelerator and sulfur are mixed in in the kneader. Mixing time: 1.5 minutes

    ______________________________________                                         Properties of the unvulcanized mixtures                                                       Mixture 1 Mixture 2                                             ______________________________________                                         t.sub.5          21.7        20.2                                              t.sub.35         27.9        24.2                                              ML 4             65          64                                                sp. gr.          1.16        1.18                                              ______________________________________                                    

    ______________________________________                                         Properties of the vulcanized mixtures                                          Vulcanization temperature: 160° C.                                      Mixture                                                                               VZ     ZF     M 300 BD   E   S    EF   A   T.sup.x)                     ______________________________________                                         1      20     157    65    575  29  57   15   81  175                          2      20     179    65    600  33  56   19   92  103                          ______________________________________                                          .sup.x) (stroke 0.250 inches)?                                           

Examples 12 shows that the organosilanes containing rubber mixtures of the invention may contain advantageously as active filler both silica and carbon black. The properties of both unvulcanized rubber mixtures (1) and (2) are practically the same and show the expert that the silica containing rubber mixture can be used on a large-scale production of tires as well as the carbon black containing rubber mixtures of the prior art.

The properties of the vulcanized mixture containing silica and carbon black show clearly better values in tensile strength, rebound, resistance to tear propagation and heat build-up on dynamic stress than the vulcanized mixture containing only carbon black. 

What is claimed is:
 1. A composition suitable for use in a rubber mixture comprising 0.1 to 50 parts of an organosilane compound having the formula

    Z -- alk -- S.sub.n -- alk -- Z,

in which Z is ##STR8## wherein R₁ is alkyl of 1 to 4 carbon atoms, cyclohexyl or phenyl and R₂ is alkoxy of 1 to 8 carbon atoms, cycloalkoxy with 5 to 8 carbon atoms or alkylmercapto with 1 to 8 carbon atoms, alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is a number of 3.0 to 6.0, and 10 to 250 parts of a siliceous filler.
 2. A composition according to claim 1 wherein Alk is a saturated aliphatic hydrocarbon, unsaturated aliphatic hydrocarbon or cycloaliphatic hydrocarbon group.
 3. A composition according to claim 2 wherein Alk has 1 to 6 carbon atoms.
 4. A composition according to claim 3 wherein Alk is a saturated aliphatic hydrocarbon group of 2 to 4 carbon atoms and n is a number of 3.0 to 4.0.
 5. A composition according to claim 2 wherein Z is (3).
 6. A composition according to claim 5 wherein Alk has 1 to 6 carbon atoms and all R₂ groups are alkoxy of 1 to 4 carbon atoms.
 7. A composition according to claim 5 wherein Alk is a saturated aliphatic hydrocarbon group of 2 to 3 carbon atoms.
 8. A composition according to claim 7 wherein the siliceous material is silica, kaolin or aluminum silicate.
 9. A composition according to claim 6 wherein the siliceous material is silica, kaolin or aluminum silicate.
 10. A composition according to claim 9 wherein the siliceous material is silica.
 11. A composition according to claim 10 wherein the silica is finely divided precipitated silica or pyrogenic silica.
 12. A composition according to claim 11 wherein the organosilane compound is 3,3'-bis-[triethoxysilyl propyl]tetrasulfide.
 13. A composition according to claim 1 wherein the organosilane has the formula ##STR9## where R₂ is alkoxy of 1 to 3 carbon atoms, Alk is alkylene of 2 to 5 carbon atoms and n is 3.0 to 4.0.
 14. A composition according to claim 1 wherein the organosilane is present as a surface coating on the siliceous filler.
 15. A composition according to claim 1 consisting of the mixture of the siliceous filler and the organosilane.
 16. A composition according to claim 1 where Z is (3), R₂ is ethoxy and alk is alkylene of 2 to 4 carbon atoms.
 17. A composition according to claim 1 wherein the siliceous filler is kaolin.
 18. A composition according to claim 1 wherein the siliceous filler is aluminum silicate.
 19. A composition according to claim 1 consisting essentially of said organosilane and said siliceous filler.
 20. A composition according to claim 1 consisting essentially of the mixture of the siliceous filler and the organosilane. 